The group A streptococcus (GAS;Streptococcus pyogenes) is a major bacterial pathogen of humans, globally causing over 700,000,000 infections and more than 500,000 deaths each year. Temperate bacteriophages are prominent genetic elements in GAS with multiple examples found in every published genome and are known to be vectors for virulence genes. However, the effect of phage integration upon host gene expression through promoter inactivation or replacement has not been explored. Our long-term goal is to understand the role of prophages in regulating host gene expression in GAS. The objective of this application is to understand how prophage SF370.4 regulates DNA mismatch repair (MMR) by altering between integrated and episomal forms in response to environmental signals. Our central hypothesis is that prophage SF370.4 acts as genetic regulator of MMR in GAS, protecting rapidly growing cells from unwanted mutations while allowing the accumulation of changes, some of which could be adaptive, when resources become limiting. Once the role of prophages as gene regulators is known, it will aid in devising new pharmacological strategies that may up- or down-regulate GAS genes so as to interfere with normal bacterial metabolism. Further, it may provide key insights into the evolution of new strains of GAS since MMR has been demonstrated to play a key role in controlling horizontal transfer. Therefore, to test our central hypothesis, the specific aims of this application are to: 1) Create isogenic prophage-free derivatives of the GAS genome strains with these prophages;and 2) Determine the contribution of each host gene regulated by the prophage to the final phenotype. The results of these studies are expected to have a positive impact, fundamentally advancing our knowledge of GAS gene regulation and evolution, and thus could lead ultimately to improved control and antimicrobial strategies. Relevance: The Streptococcus pyogenes is an important cause of bacterial disease in humans. This research will determine the role of a bacterial virus in regulating a key DNA repair system. The results will increase our understanding of evolution and gene regulation in this bacteria and thus aid in devising new antimicrobial strategies. Further, in keeping with the goals of AREA grants, we will continue to provide research opportunities for professional and pre-professional as we have over the first funding period of this research. PUBLIC HEALTH RELEVANCE: Significance to Public Health The group A streptococcus is an important cause of bacterial disease in humans. This research will determine the role of a bacterial virus in regulating a key DNA repair system. The results will increase our understanding of evolution and gene regulation in this bacteria and thus aid in devising new antimicrobial strategies.